Decorating anodized metal with dye imbibition transferred images

ABSTRACT

DECORATING ANODIZED METALS, SUCH AS ALUMINUM, BY EXPOSING SAID ANODIZED METAL SUBSTRATE BEARING A LIGHTSENSITIVE LAYER TO ACTINIC RADIATION TO ESTABLISH A POTENTIAL RD OF 0.2 TO 2.2, APPLYING A DRY POWDER COMPRISING A WATER SOLUBLE DRY TO THE LIGHT-SENSITIVE LAYER, EMBEDDING THE DEVELOPING POWDER IN IMAGE-WISE CONFIGURATION INTO THE LIGHT-SENSITIVE LAYER, REMOVING THE DEVELOPING POWDER FROM THE NON-IMAGE AREAS AND MOLECULARLY IMBIBING AND TRANSPORTING SAID DYE FROM THE DRY POWDER INTO THE PORES OF THE ANODIZED METAL IN IMAGE-WISE CONFIGURATION BY CONTACTING SAID LIGHT-SENSITIVE LAYER WITH WATER VAPOR.

United States Patent Office Patented Oct. 17, 1972 3,698,905 DECORATINGANODIZED METAL WITH DYE IMBIBITION TRANSFERRED IMAGES Warren Guy VanDorn and James Maurice Hardenbrook,

Columbus, Ohio, assignors to A. E. Staley Manufacturing Company,Decatur, Ill. No Drawing. Filed Mar. 23, 1971, Ser. No. 127,354 Int. Cl.G03c 5/00, 7/00; G03f 3/04 US. Cl. 96-48 R 11 Claims ABSTRACT OF THEDISCLOSURE Decorating anodized metals, such as aluminum, by exposingsaid anodized metal substrate bearing a lightsensitive layer to actinicradiation to establish a potential R, of 0.2 to 2.2, applying a drypowder comprising a water soluble dye to the light-sensitive layer,embedding the developing powder in image-wise configuration into thelight-sensitive layer, removing the developing powder from the non-imageareas and molecularly imbibing and transporting said dye from the drypowder into the pores of the anodized metal in image-wise configurationby contacting said light-sensitive layer with water vapor.

DISCLOSURE OF THE INVENTION This invention relates to a method ofdecorating anodized metals.

The production of designs or decorations on anodized metals, usuallyaluminum, is of particular interest for the production of individualnameplates for attachment to machines. To a lesser extent thesedecorated metals are of interest for use as panels in the constructionof buildings, for beverage cans, etc. Anodized metal surfaces have beendecorated previously by applying a film of colorant from lacquers,varnishes and the like. Due to the extremely minute pores in anodizedsurfaces, most lacquers, varnishes or the like form a surface layer ontop of the anodized metal. Such films are subject to deterioration sincethey can be removed by abrasion and are often opaque or even whentransparent, the conventional coatings detract somewhat from the beautyof the anodized surface itself.

Anodized metals have also been decorated by dyeing, typically by dippingthe anodized metal in a dye bath to provide a single overall color. Oneor more colors have also been applied to predetermined areas of anodizedmetals by applying photochemical resists to the anodized metal,exposing, to light to tan the resist in the exposed areas, washing outthe unexposed areas and dipping the anodized metal in a dye bath. Suchtechniques have the disadvantage that they require complete removal ofthe unexposed areas before dipping in the dye bath and complete removalof the tanned resist after the application of the dye. These removalsteps are complicated by the porous nature of the anodized metal and thecrosslinked nature of the tanned resist. Further, since mostlight-sensitive layers capable of forming resists are inherentlynegative acting, it is usually necessary to employ a negative of thedesign or image to be reproduced on the predetermined layer.

US. Pat. 3,484,342 indicates that multi-color anodized aluminum objectscan be prepared by printing a multicolor-mirror-dye-image on a papersurface and then transferring the dye image by sublimation from theprinted sheet to the anodized aluminum surface. However, this techniquehas all the disadvantages inherent in conventional printing processes,plus the additional disadvantages inherent in the production of mirrorimages on the paper surface and, as explained in the patent, the rigidrequirements on the dyes that may be utilized in the process. Further,this process is uneconomical for the production of relatively smallquantities of high quality decorated nameplates.

The general object of this invention is to provide a direct method ofproducing decorated anodized materials. Another object of this inventionis to provide a direct method of producing individual decorated anodizedaluminum nameplates. Other objects will appear hereinafter.

We have now found that the objects of this invention can be attained byexposing an anodized metal bearing a light-sensitive layer protrudingabove the peaks of the anodized metal, capable of developing a R of 0.2to 2.2 of the type described and claimed in commonly assignedapplication, Ser. No. 796,897, filed Feb. 5, 1969, to actinic radiationto establish a potential R, of 0.2 to 2.2, applying a dry powdercomprising a water-soluble dye or dyes to the exposed light-sensitivelayer, embedding the developing powder in image-wise configuration intothe light-sensitive layer, treating the light-sensitive element withwater vapor (moist warm air) to imbibe the dye or dyes from the drypowder into the pores of the anodized metal in image-wise configuration.The anodized aluminum layer acts as a receiving layer much like thewater-swellable receiving layers described in aforementioned applicationSer. No. 796,897.

In the preferred method of operation, it is desirable to apply ahydrophilic colloid to the anodized metal surface prior to theapplication of the light-sensitive composition. The hydrophilic layertends to fill up the pores of the anodized metal and prevent thelight-sensitive composition from working into the pores of the anodizedmetal with the result that a more uniform light-sensitive layer isproduced for subsequent steps in the process. Failure to use ahydrophilic colloid to at least partially fill up the pores of theanodized aluminum object necessitates the application of a substantiallythicker layer of light-sensitive material in order to fill up the poresof the anodized metal with sensitizer. It is essential in this inventionthat the hydrophilic colloid only fill up the pores of the anodizedmetal and not form a thick layer over the anodized surface. If thehydrophilic colloid forms a thick layer, the hydrophilic colloid acts asa receiving layer for the dye imbibition step and insufficient dyepenetrates into the pores of the anodized metal. In such case, the imageis above the surface of the anodized metal and the image intensity dropsmarkedly when the hydrophilic colloid is removed. On the other hand,when the hydrophilic colloid fills up part or all of the pores of theanodized metal, there is substantially no loss in dye intensity when theanodized object is washed with water and substantially all of thehydrophilic colloid removed from the' surface of the anodized object. Inthis case, the dye is imbibed into the anodized metal.

In somewhat greater detail, the anodized metal, preferably anodizedaluminum containing a hydrophilic colloid filling up at least part ofthe pores of the anodized metal, is decorated by coating the anodizedmetal with a lightsensitive layer capable of developing R of 0.2 to 2.2,preferably 0.4 to 2.0, exposing the element to actinic ra diation toestablish a potential R of 0.9 to 2.2, applying a dry powder comprisinga water-soluble dye or dyes to the exposed light-sensitive layer,embedding the developing powder in image-wise configuration into thelight-sensitive layer, treating the light-sensitive layer with Watervapor (moist warm air) to imbibe the dye or dyes from the dry powderinto the pores of the anodized metal in imagewise configuration. Thesensitizer and developing powder remaining on the surface of thehydrophilic layer are removed with a solvent.

When this invention is employed to produce objects having three or morecolors (the first color being anodized metal surface and the secondcolor being the first imbibed dye image), it is desirable to employ awater-insoluble sensitizer and remove sensitizer layer and embeddedcarrier powder particles from the surface of the anodized metal bywashing with a suitable solvent for the sensitizer. In general, it isalso preferred that the solvent be capable of dissolving the carrier forthe developing powder. However, solvent insoluble carriers will beremoved at the same time as the light-sensitive layer in any case. Theanodized metal layer, preferably bearing the hydrophilic colloidal layeris then resensitized, exposed to light to a second pattern, developedwith a second developing powder comprising a second dye or dyes and thesecond dye or dyes imbibed into the anodized surface. This technique maybe repeated as many times as desired. If the pores of the anodized metalare filled with a hydrophilic colloid prior to dye imbibition, it ispreferred that the hydrophilic colloid be removed by a simple waterwashing step after the last dye image is imbibed into the anodizedmetal. At this point the anodized metal may be sealed, if desired, orleft unsealed.

The pores of the anodized metal are at least partially filled byapplying an aqueous solution or dispersion of a suitable hydrophiliccolloid by any means dictated by the nature of the colloidalcomposition, such as by spray, roller coating or air knife, flow, dip orwhirler coating, curtain coating, etc. For example, a 0.1 to 30% byweight aqueous solution or dispersion of hydrophilic colloid can be flowcoated over the surface of the anodized metal using a rod, wire wrappedrod, doctor blade, etc. to assure that the hydrophilic colloid does notprotrude above the surface of the anodized metal but only fills thepores thereof.

Suitable hydrophilic colloids include polyvinyl alcohol, starch,hydroxyethyl starch, carboxyrnethyl starch, cyanoethyl starch,hydroxyethyl cellulose, carboxymethyl cellulose, gelatin, gumtragacanth, gum arabic, dextrin, dextran, Carbopol (carboxypolymethylene), etc. Of these, the cold Water soluble hydroxy containingpolymers free of carboxyl groups such as polyvinyl alcohol are preferredsince these materials can be readily removed from the pores of theanodized metal after the dye imbibition of colorant or colorants. The'carboxyl containing materials have the disadvantage that they chemicallybond to the anodized metal and are not readily removed with cold water.

The light-sensitive layers are formed by applying a thin layer of solid,light-sensitive, film-forming organic material having a potential R of0.2 to 2.2 to the anodized layer, preferably anodized metal having ahydrophilic col loid filling up at least part of the pores of theanodized metal, by any suitable means dictated by the nature of thefilm-forming material (hot-metal, draw down, spray, roller coating orair knife, flow, dip or whirler coating, curtain coating, etc.) so as toproduce a reasonably smooth homogeneous layer projecting from 0.1 to 40microns above the peaks of the anodized metal employing suitablesolvents as necessary.

As indicated above, the light-sensitive elements employed in thisinvention have a R of 0.2 to 2.2. If the R is below 0.2 thelight-sensitive layer is too hard to accept a suitable concentration ofpowder particles. On the other hand, if the R is above 2.2, thedeveloping powder will not embed as a monolayer and the light-sensitivelayer may stick to the transparency in vacuum frame exposure equipment.The R of positive-acting, light-sensitive layers, which is called R is aphotometric measurement of the reflection density of a black powderdeveloped light-sensitive layer after a positive-acting, light-sensitivelayer has been exposed to suflicient actinic radiation to convert theexposed areas into substantially powder-non-receptive state (clear thebackground). The R of a negative-acting, light-sensitive layer, which iscalled R is a photometric measurement of the reflection density of ablack powder developed area, after a negative-acting, light-sensitivelayer has been exposed to suflicient actinic radiation to convert theexposed areas into a powder-receptive state.

The reflection density of a solid, positive-acting, lightsensitive layer(R is determined by coating the lightsensitive layer on a whitesubstrate, exposing the lightsensitive layer to suflicient actinicradiation image-wise to clear the background of the solid,positive-acting, lightsensitive layer, applying a black powder (preparedfrom 77% Pliolite VTL and 23% Neo Spectra carbon black in the mannerdescribed below) to the exposed layer, physically embedding said blackpowder under the conditions of development as a monolayer in a stratumat the surface of said light-sensitive layer and removing thenonembedded particles from said light-sensitive layer. The developedorganic layer containing black powder embedded image areas andsubstantially powder free non-image areas is placed in a standardphotometer having a scale reading from 0 to reflection of incident lightor an equivalent density scale, such as on Model 500 A photometer of thePhotovolt Corporation. The instrument is zeroed (0 density; 100%reflectance) on a powder free nonimage area of the light-sensitiveorganic layer and an average R reading is determined from the powderdeveloped area. The reflection density is a measure of the degree ofblackness of the developed surface which is relatable to theconcentration of particles per unit area. The reflection density of asolid, negative-acting, light-sensitive layer (R is determined in thesame manner except that the negative-acting, light-sensitive layer isexposed to sufficient actinic radiation to convert the exposed area intoa powder-receptive area. If the R under the conditions of development isbetween 0.2 to 2.2, the solid, light-sensitive organic materialdeposited in a layer is suitable for use in this invention.

Although the R of light-sensitive layers is determined by using theaforesaid black developing powder and a white substrate, the R is only ameasure of the suitability of a light-sensitive layer for use in thepresent invention.

Since the R of any light-sensitive layer is dependent on numerousfactors other than the chemical constitution of the light-sensitivelayer, the light-sensitive layer is best defined in terms of its R underthe development conditions of intended use. The positive-acting, solid,lightsensitive organic layers useful in this invention must be powderreceptive in the sense that the aforesaid black developing powder can beembedded as a monoparticle layer into a stratum at the surface of theunexposed layer to yield a R of 0.2 to 2.2 (0.4 to 2.0 preferably) underthe predetermined conditions of development and lightsensitive in thesense that upon exposure to actinic radiation the most exposed areas canbe converted into the nonparticle receptive state (background cleared)under the predetermined conditions of development. In other words, thepositive-acting, light-sensitive layer must contain a certain inherentpowder receptivity and light-sensitivity. The positive-acting,light-sensitive layers are apparently converted into thepowder-non-receptive state by a light-catalyzed hardening action, suchas photopolymerization, photocrosslinking, photooxidation, etc. Some ofthese photohardening reactions are dependent on the presence of oxygen,such as the photooxidation of internally ethylenically unsaturated acidsand esters, while others are inhibited by the presence of oxygen, suchas those based on the photopolymerization of vinylidene orpolyvinylidene monomers alone or together with polymeric materials. Thelatter requires special precautions, such as storage in oxygen-freeatmosphere or oxygen-impermeable cover sheets. For this reason, it ispreferable to use solid, positive-acting, film-forming organic materialscontaining no terminal ethylenic unsaturation.

The negative-acting, solid, light-sensitive organic layers useful inthis invention must be light-sensitive in the sense that, upon exposureto actinic radiation, the most exposed areas of the light-sensitivelayer are converted from a nonpowder-receptive state under thepredetermined conditions of development. to a powder-receptive stateunder the predetermined conditions of development. In other words, thenegative-acting, light-sensitive layer must have a certain minimumlight-sensitivity and potential powder receptivity. The negative-acting,light-sensitive layers are apparently converted into the powderreceptive state by a light-catalyzed softening action, such asphotodepolymerization, photoisomerization, etc.

In general, the positive-acting, solid, light-sensitivelayers useful inthis invention comprise a film-forming organic material in its naturallyoccurring or manufactured form or a mixture of said organic materialwith plasticizers and/or photoactivators for adjusting powderreceptivity and sensitivity to actinic radiation. Suitablepositive-acting, film-forming organic materials which are not inhibitedby oxygen, include internally ethylenically unsaturated acids, such asabietic acid, rosin acids, partially hydrogenated rosin acids, such asthose sold under the name Staybelite resin, wood rosin, etc., esters ofinternally ethylenically unsaturated acids, methylol amides of maleatedoils such as described in US. Pat. 3,471,466, phosphatides of the classdescribed in application Ser. No. 796,841, filed on Feb. 5, 1969, nowUS. Pat. 3,585,- 031, in the name of Hayes, such as soybean lecithin,partially hydrogenated lecithin, dilinolenyl-alpha-lecithin, etc.,partially hydrogenated rosin acid esters, such as those sold under thename Staybelite esters, rosin modified alkyds, etc.; polymers ofethylenically unsaturated monomers, such as vinyltoluene-alpha methylstyrene copolymers, polyvinyl cinnamate, polyethyl methacrylate, vinylacetatevinyl stearate copolymers, polyvinyl pyrrolidone, etc.; coal tarresins such as coumarone-indene resins, etc.; halogenated hydrocarbons,such as chlorinated waxes, chlorinated polyethylene, etc.Positive-acting, light-sensitive materials, which are inhibited byoxygen include mixtures of polymers, such as polyethyleneterephthalate/sebacate, or cellulose acetate or acetate/butyrate, withpolyunsaturated vinylidene monomers, such as ethylene glycol diacrylateor dimethacrylate, tetraethylene glycol diacrylate or dimethacrylate,etc.

Although numerous positive-acting, film-forming organic materials havethe requisite light-sensitivity and powder-receptivity at predetermineddevelopment temperatures, it is generally preferable to compound thefilmforming organic material with photoactivator(s) and/ orplasticizer(s) to impart optimum powder receptivity andlight-sensitivity to the light-sensitive layer. In most cases, thelight-sensitivity of an element can be increased many fold byincorporation of a suitable photoactivator capable of producingfree-radicals, which catalyze the lightsensitive reaction and reduce theamount of photons necessary to yield the desired physical change.

Suitable photoactivators capable of producing free-radicals includebenzil, benzoin, Michlers ketone, diacetyl, phenanthraquinone,p-dimethylaminobenzoin, 7,8-benzoflavone, trinitrofluorenone,desoxybenzoin, 2,3-pentanedione, dibenzylketone, nitroisatin,di(6-dimethylamino-3- pyradil) methane, metal naphthanates,N-methyl-N-phenylbenzylamine, pyridil, 5,7-dichloroisatin,azodiisobutyronitrile, trinitroanisole, chlorophyll, isatin,bromoisatin, etc. These compounds can be used in a concentration of .001to 2 times the weight of the film-forming organic material (.1%200% theweight of film former). As in most catalytic systems, the bestphotoactivator and optimum concentration thereof is dependent upon thefilm-forming organic material. Some photoactivators respond better withone type of film former and may be useful with substantially allfilm-formers in wide concentration ranges.

The acyloin and vicinal diketone photoactivators, particularly benziland "benzoin are preferred. Benzoin and benzil are effective over wideconcentration ranges with substantially all film-forming,light-sensitive organic materials. Benzoin and benzil have theadditional advantage that they have a plasticizing or softening effecton filmforming, light-sensitive layers, thereby increasing the powderreceptivity of the light-sensitive layers. When employed as aphotoactivator, benzil should preferably comprise at least 1% by weightof the film-forming organic material (.01 times the film former weight).

Dyes, optical brighteners and light absorbers can be used alone orpreferably in conjunction with the aforesaid free-radical producingphotoactivators (primary photoactivators) to increase thelight-sensitivity of the light-sensitive layers of this invention byconverting light rays into light rays of longer lengths. Forconvenience, these secondary photoactivators (dyes, optical brightenersand light absorbers) are called superphotoactivators. Suitable dyes,optical brighteners and light absorbers include4-methyl-7-dimethylaminocoumarin, Calcofiuor yellow HEB (preparationdescribed in US. Pat. 2,415,373), Calcofluor white SB super 30080,Calcofluor, Uvitex W. conc., Uvitex TXS conc., Uvitex RS (described inTextil- Rundschau 8 [1953], 339), Uvitex WGS conc., Uvitex K, Uvitex CFconc., Uvitex W (described in Textil-Rundschau 8 [1953], 340 Aclarat8678, Blancophor OS, Tenopol UNPL, MDAC 8-8844, Uvinul 400 ThilflavinTGN conc., Aniline yellow-S (low conc.), Seto Flavine T 5506-140,Auramine O, Calcozine yellow 0X, Calcofluor RW, Calcofluor GAC, Acetosolyellow 2 -RLS-PHF, Eosine bluish, Chinoline yellow-P conc., Cenilineyellow S (high conc.), Anthracene blue Violet fluorescence, Calcofiuorwhite MR, Tenopol PCR, Uvitex GS, Acid-yellow-T- supra, Acetosol yellow5 GLS, Calcocid OR. Y. Ex. conc., diphenyl brilliant fiavine 7 GFF,Resofiorm fluorescent yellow 3 GPI, Eosin yellowish, Thiazole fluorescorG, Pyrazalone organe YB-3, and National FD & C yellow. Individualsuperphoto activators may respond better with one type oflight-sensitive organic film former and photoactivator than with others.Further, some photoactivators function better with certain classes ofbrighteners, dyes and light absorbers; For the most part, the mostadvantageous combinations of these materials and proportions can bedetermined by simple experimentation.

As indicated above, plasticizers can be used to impart optimum powderreceptivity to the light-sensitive layer. With the exception oflecithin, most of the film-forming, llght-sensitive organic materialsuseful in this invention are not powder-receptive at room temperaturebut are powder-receptive above room temperature. Accordingly, It isdesirable to add sufiicient plasticizer to impart room temperature (15to 30 C.) or ambient temperature powder-receptivity to thelight-sensitive layers and/or increase the R range of thelight-sensitive layers.

While various softening agents, such as dimethyl phthalate, glycerol,vegetable oils, etc. can be used as plasticizers, benzil and benzoin arepreferred since, as pointed out above, these materials have theadditional advantage that they increase the light-sensitivity of thefilm-forming organic material. As plasticizer-photoactivators, benzoinand benzil are preferably used in a concentration of 1% to by weight ofthe film-forming solid organic maer1a The preferred positive-acting,light-sensitive film formers containing no conjugated terminal ethylenicunsaturation include the esters and acids of internally ethylenicallyunsaturated acids, particularly the phosphatides, rosin acids, partiallyhydrogenated rosin acids and the partially hydrogenated rosin esters.These materials, when compounded with suitable photoactivators,preferably acyloins or vicinal diketones together withsuperphotoactivators, require less than 2 minutes exposure to clear thebackground of light-sensitive layers.

In general, the negative-acting, light-sensitive layers useful in thisinvention comprise a film-forming organic material in its naturallyoccurring or manufactured form, or a mixture of said organic materialwith plasticizers and/ or photoactivators for adjusting powderreceptivity and sensitivity to actinic radiation. Suitablenegative-acting,

film-forming organic materials include n-benzyl linoleamide,dilinoleyl-alpha-lecithin, castor wax (glycerol 12- hydroxy-stearate),ethylene glycol monohydroxy stearate, polyisobutylene, polyvinylstearate, etc. Of these, castor wax and other hydrogenated ricinoleicacid esters (hydroxystearate) are preferred. These materials can becompounded with plasticizers and/or photoactivators in the same manneras the positive-acting, light-sensitive, filmforming organic materials.

Some solid, light-sensitive organic film formers can be used to prepareeither positive or negative-acting, lightsensitive layers. For example,a poly(n-butyl methacrylate) layer containing 20 percent benzoin (20parts by Weight benzoin per 100 parts by weight polymer) yields goodpositive-acting images. Increasing the benzoin level to 100 percentconverts the poly(n-butyl methacrylate) layer into a goodnegative-acting system.

The light-sensitive layer must protrude at least 0.1 micron above thepeaks of the anodized metal and preferably at least 0.4 micron in orderto hold suitable powders during the development. If the light-sensitivelayer protrudes less than 0.1 micron, or the developing powder diameteris more than 25 times layer thickness, the lightsensitive layer does nothold the developing powder with the necessary tenacity. In general, aslayer thickness increases, the light-sensitive layer is capable ofholding larger particles. However, as the light-sensitive layerthickness increases, it becomes increasingly difiicult to maintain filmintegrity during film development. Accordingly, the light-sensitivelayer must protrude from 0.1 to 40 microns above the peaks of theanodized metal, preferably from 0.4 to 2.5 microns.

The preferred method of applying light-sensitive layers of predeterminedthicknesses to the anodized metal (including anodized metal filled withhydrophilic colloid) comprises flow coating a solution in an organicsolvent vehicle (hydrocarbons, such as hexane, heptane, benzene, etc.;halogenated hydrocarbons, such as chloroform, carbon tetrachloride,1,1,1-trichloroethane, trichloroethylene, etc.; alcohols, such asethanol, methanol, isopropanol, etc.; ketones, such as acetone, methylethyl ketone, etc.) of the light-sensitive organic film-former alone ortogether with dissolved or suspended photoactivators or plasticizersonto the base. The hydrocarbons and halohydrocarbons, which areexcellent solvents. for the preferred positiveacting, light-sensitivefilm formers, containing no terminal conjugated ethylenic unsaturation,are the preferred vehicles because of their high volatility and lowcost. Typically, solutions prepared with these vehicles can be appliedto the base and air dried to a continuous clear film in less than oneminute. In general, the halohydrocarbons have the advantage that theyare non-flammable and can be used without danger of flash fires.However, many of these, such as chloroform and carbon tetrachloride mustbe handled with care due to the toxicity of their vapors. Of all thesesolvents, 1,1,1-trichloroethane is preferred since it has low toxicity,is non-flammable, low cost and has high volatility. In general, thethickness of the light-sensitive layer can be varied as a function ofthe concentration of the solids dissolved in the solvent vehicle.

After the anodized metal is coated with a suitable solid,light-sensitive organic layer, a latent image is formed by exposing theelement to actinic radiation in image-receiving manner for a timesuflicient to provide a potential R of 0.2 to 2.2 (clear the backgroundof the positive-acting, light-sensitive layers or establish a potentialR of 0.2 to 2.2 with negative-acting, light-sensitive layers). Thelightsensitive elements can be exposed to actinic radiation through aphotographic positive or negative, which may be line, half-tone orcontinuous tone.

As indicated above, the latent images are preferably produced frompositive-acting, light-sensitive layers by exposing the element inimage-receivin g manner for a time sufficient to clear the background,i.e. render the exposed areas non-powder-receptive. As explained incommon-1y assigned application Ser. No. 796,847, now U.S. Pat.3,637,385, the amount of actinic radiation necessary to clear thebackground varies to some extent with developer powder size anddevelopment conditions. Due to these variations it is often desirable toslightly overexpose line and half-tone images in order to assurecomplete clearing of the background. Slightly more care is necessary inproducing continuous-tone powder images since overexposure tends todecrease the tonal range of the developed image. In general,overexposure is preferred with negative-acting, light-sensitive elementsin order to provide maximum contrast.

After the light-sensitive element is exposed to actinic radiation for atime sufficient to clear the background of a positive-acting,light-sensitive layer or establish a potential R of 0.2 to 2.2, adeveloping powder having a diameter or dimension along one axis of atleast 0.3 micron comprising a dye is applied physically with a suitableforce, preferably mechanically, to embed the powder in thelight-sensitive layer. The developing powder can be virtually any shape,such as spherical, acicular, platelets, etc.

The developing powders suitable for use in dye imbibition imagingprocesses comprises one or more water-soluble dyes. Generally the dye ordyes are on a solid carrier in order to control the particle size of thedeveloping powder and to control the intensity of the final dye image.The dye or dyes can be ball-milled with the solid carrier in order tocoat the carrier with dye. If desired, dyes can be blended above themelting point with various solid carriers, ground to suitable size andclassified. In some cases it is advantageous to dissolve dye and carrierin a mutual solvent, dry and grind to suitable size. Preferably, thecarrier is coated with dye, since the dye is more readily and moreefiiciently embedded into the substrate. If the dye is in the carriermatrix, more dye must be employed to obtain comparable brilliance andimage density. However, the latter route tends to preclude individualdye particles from embedding in nonimage areas.

Suitable solid carriers include polymeric or resinous materials, such asPliolite VTL (vinyltoluene-butadiene copolymer), polymethylmethacrylate, polystyrene, rice starch, corn starch, phenol-formaldehyderesins, etc.; organic monomeric compounds such as hydroquinone,sorbitol, manitol, dextrose, tartaric acid, urea, animal glue, gelatin,g-um arabic, Carbowaxes, polyvinyl pyrrolidone, etc. Suitable metalpowders include aluminum flakes, nickel flakes, rhodium powders, etc.

For use in this invention, it is generally preferred that the solidcarrier is water insoluble and organic solvent soluble. In this way,none of the solid carrier migrates into the pores of the anodized metalduring the dye imbibition step and the solid carrier can subsequently beremoved readily with solvent solution to restore the originalcharacteristics of the anodized metal for the next image.

Suitable water soluble dyes include Alphazurine 2G, Calcocid Phloxine2G, Tartrazine, Acid Chrome blue 3BA Conc., Acid Magenta 0., Ex. Conc.,Neptune Blue BRA Conc., Nigrosine, Jet Conc., Patent Blue AF, Ex. Conc.,Pontacyl Light Red 4 'BL Cone. etc.

The black developing powder for determining the R of a light-sensitivelayer is formed by heating about 77% Pliolite VTL(vinyl-toluene-butadiene copolymer) and 23% Neo Spectra carbon black ata temperature above the melting point of the resinous carrier, blendingon a rubber mill for fifteen minutes and then grinding in aMikro-atomizer.

The developing powders useful in this invention contain particles havinga diameter or dimension along at least one axis from 0.1 to 40 microns,preferably from 0.5 to 15 microns with powders of the order of 1 to 15microns being best for light-sensitive layers of 0.4 to 10 microns.Maximum particle size is dependent on the thickness of light-sensitivelayer while minimum particle size is independent of layer thickness.Electron microscope studies have shown that developing powders having adiameter 25 times the thickness of the light-sensitive layer cannot bepermanently embedded into light-sensitive layers, and generallyspeaking, best results are obtained where the diameter of the powderparticle is less than about times the thickness of the light-sensitivelayer. For the most part, particles over 40 microns are not detrimentalto image development provided the developing powder contains areasonable concentration of powder particles under 40 microns, which areless than 25 times, and preferably less than 10 times, thelight-sensitive layer thickness. However, other things being equal, thelarger the developer powder particles (above 10 microns), the lower theR of the developed image.

Although particles over 40 microns are not detrimental to imagedevelopment, the presence of particles under 0.1 micron diameter alongall axes can be detrimental to proper image formation. In general, it ispreferable to employ developing powders having substantially all powdershaving a diameter along at least one axis not less than 0.3 micron,preferably more than 0.5 micron, since particles less than 0.3 microntend to embed in nonimage areas. As the particle size of the smallestpowder in the developer increases, less exposure to actinic radiation isrequired to clear the background.

In general, somewhat more deposition of powder particles into non-imageareas can be tolerated when using a black developing powder than acolored powder, since the human eye is less offended by gray backgroundon non-image areas than by the deposition of colored particles innon-image areas. Therefore, the concentration of particles under 0.1micron and the size of the developing powder is more critical when usinga cyan, magenta or yellow developing powder. For best results, thedeveloping powder should have substantially all particles (at least 95%by weight) over 1 micron in diameter along one axis and preferably from1 to microns for use with light-sensitive layers of from 0.4 to 10microns. In this way, powder embedment in image areas is maximum andrelatively little powder is embedded into non-image areas.

In somewhat greater detail, the developing powder is applied directly tothe light-sensitive layer, while the powder receptive areas of saidlayer are in at most only a slightly soft deformable condition and saidlayer is at a temperature below the melting point of the layer andpowder. The powder is distributed over the area to be developed andphysically embedded into the stratum at the surface of thelight-sensitive layer, preferably mechanically by force having a lateralcomponent, such as to-and-fro and/or circular rubbing or scrubbingaction using a soft pad or fine brush. If desired, the powder may beapplied separately or contained in the pad or brush. The quantity ofpowder is not critical provided there is an excess available beyond thatrequired for full development of the area, as the development seems todepend primarily on particle-to-particle interaction rather thanbrush-to-surface or pad-to-surface forces to embed a layer of powderparticles substantially one particle thick (monoparticle layer) into astratum at the surface of the light-sensitive layer. When viewed underan inverse microscope, spherical powder particles under about 10 micronsin diameter enter the powder-receptive areas first and stop dead,embedded substantially as a monolayer. The larger particles seem totravel over the embedded smaller particles which do not rotate or moveas a pad or brush is moved back and forth over the developed area.Non-spherical particles, such as platelets, develop like the sphericalpowders except that the fiat side tends to embed. Only a single stratumof powder particles penetrates into the powder-receptive areas of thelight-sensitive layer even if the light-sensitive layer is several timesthicker than the developer particle diameter.

After the powder application, excess powder remains on the surface whichhas not been sufiiciently embedded into, or attached to, the film. Thismay be removed in any convenient way, as by wiping with a clean pad orbrush usually using somewhat more force than employed in mechanicaldevelopment, by vacuum, by vibrating, or by air doctoring. Forsimplicity and uniformity of results, the excess powder is usually blownoff using an air gun having an air-line pressure of about 20 to 40p.s.i.

At this point the powder particles comprising a water soluble dye, heldin image-wise configuration in particulate form in the light-sensitivelayer, are separated from the anodized metal by the light-sensitivelayer. An aesthetically more pleasing image is then produced by treatingthe developed image with water vapor, molecularly imbibing said dye intothe anodized metal. Other things being equal, the particulate dye imagechanges from a pale or pastel color to a brilliant, saturated, morepleasing hue. The light-sensitive layer, which preferably contains noconjugated terminal ethylenic unsaturation, is then removed from thesurface of the anodized metal with a solvent for the light-sensitivelayer which is a poor solvent for the surface of the substrate.1,1,1-trichloroethane is particularly well suited for use in this step.Removal of the light-sensitive layer and the carrier for the developingpowder renews the surface of the anodized metal so that it can beresensitized with a substantially even layer of sensitizer.

As indicated above, the water soluble dye is separated from the anodizedmetal by the light-sensitive layer. Although the transportation of thedye through the solid, organic layer is not completely understood, it isbelieved that in most cases dye imbibition is due to weakening of thelight-sensitive layer by the powder particles employed duringdeformation imaging creating potential points of stress in the filmsurface. Subsequently, when the water vapor contacts the light-sensitivelayer, a second stress is imposed upon the light-sensitive layerresulting in fracturing of the light-sensitive layer and transportationof the dye through the light-sensitive layer and imbibition of said dyeinto the anodized metal pores. In other cases dye imbibition may be dueto water vapors diffusing the dissolved dye into the light-sensitivelayer. In any event, the water vapor must be capable of transporting thedye through the organic light-sensitive layer.

Experiments have shown that the development of various light-sensitiveelements, such as Staybelite Ester #10 and Staybelite resin, withdeveloping powder weakens the film layer. For example, when theselight-sensitive elements are developed with undyed developing powder, itis possible to imbibe water soluble dye into the receiving layer inimage-wise configuration by merely dipping the developed light-sensitiveelement into an aqueous dye bath. In such case the water soluble dyeenters the hydrophilic receiving layer in the areas defined by theundyed powder particles. Accordingly, in such case, it is clear thattransportation of the dye through the light-sensitive layer is at leastpartially due to weakening of the light-sensitive layer by developerparticle.

It has also been found that the above light-sensitive materials have atendency to puddle up in the exposed areas in image-wise configurationwhen merely exposed to light and treated with water vapors. Accordingly,dye imbibition of water-soluble dyes through these materials is alsopartially due to the ability of moist warm air to disrupt the unexposedareas of the light-sensitive layer. In other cases, such as in the caseof phosphatide lightsensitive elements, the exposed areas of thelight-sensitive layer are converted into a more water-soluble conditionthan the unexposed areas as explained in aforementioned copendingapplication, Ser. No. 796,841 of Hayes, filed Feb. 5, 1969, now U.S.Pat. 3,585,031. In such case, water vapor tends to transport the dyeimage through the exposed areas of the light-sensitive element with theresult that the original positive powder image changes into a negativedye imbibition image. In still other cases, it has been possible toprevent passage of water-soluble dye into the dye imbibition receivinglayer by adding various hydrophobic agents, such as silicone oils in aconcentration of 200 parts per million to various light-sensitivelayers, such as those based on Staybelite resins and esters. Thesilicone tends to act as a waterproofing agent in this environment andno dye imbibition with water vapor is possible since water vapor isincapable of transporting the dye through the lightsensitive layer. Dyeimbibition of water-soluble dye through light-sensitive layers based onpoly(n-butyl methacrylate) and other high molecular weight hydrophobicpolymers, is relatively diflicult due to the extreme hydrophobic natureof these film formers. Accordingly, routine experimentation may becarried out to determine which aqueous solvents are best fortransporting specific dyes through particular light-sensitive elements.

The preferred method of forming multi-colored reproductions comprisescoating anodized aluminum containing a hydrophilic colloid filling upthe pores of the anodized metal with a halohydrocarbon solution of alight-sensitive organic film former containing no conjugated terminalethylenic unsaturation to form a light-sensitive layer protruding fromabout 0.5 to 2.5 microns above the peaks of the anodized metal, capableof developing a R of 0.4 to 2.0; exposing said light-sensitive organiclayer to actinic radiation in image-receiving manner to establish apotential R, of 0.4 to 2.0; applying to said layer of organic material,free-flowing powder particles comprising a water-soluble dye and a 1,1,1trichloroethane soluble carrier, said powder particles having a diameteralong at least one axis of at least one micron; while the element is ata temperature below the melting points of the powder and the organiclayer, physically embedding said powder particles as a monolayer in astratum at the surface of said light-sensitive layer to yield an imagehaving portions varying in density in proportion to the exposure of eachportion; removing non-embedded particles from said organic layer todevelop an image; molecularly imbibing water-soluble dye into the poresof the anodized metal by contacting the particles embedded in saidorganic layer with vapors of Water or steam; removing saidlight-sensitive organic film former containing no conjugated terminalethylenic unsaturation and the carrier for said dye with 1,1,1trichloroethane clearing agent; coating the substrate bearing the firstcolor in image-wise configuration in the surface of said substrate witha solid, light-sensitive organic film former containing no conjugatedterminal ethylenic unsaturation from a 1,1,1-trichloroethane vehicle toform a second light-sensitive organic layer protruding from about 0.5 to2.5 microns above the peaks of the anodized metal, capable of developinga R of 0.4 to 2.0; exposing said light-sensitive layer to actinicradiation in image-receiving manner to establish a potential R of 0.4 to2.0; applying to said layer of organic material free-flowing powderparticles comprising a second Water soluble dye and carrier, said powderparticles having a diameter along one axis of at least one micron; whilethe layer is at a temperature below the melting points of the powder andof the organic layer, physically embedding said powder particles as amonolayer in a stratum at the surface of said second light-sensitivelayer to yield an image having portions varying in density in proportionto the exposure of each portion; removing the non-embedded particlesfrom said organic layer to develop a three color reproduction (two dyeimages on an aluminum background); molecularly imbibing water solubledye into the anodized layer by contacting the particles embedded in saidorganic layer with vapors of Water or steam; removing said secondlightsensitive layer and second developer powder layer with1,1,l-trichloroethane clearing solution and repeating the process to putdown a third, fourth, fifth dye image. After the last image is put down,the hydrophilic colloid is pref- 12 erably removed by flowing water overthe surface of the imaged anodized metal or by placing the anodizedmetal in a suitable water bath. Alternatively, the hydrophilic colloidmay be left in the pores of the anodized metal.

If desired, after the first dye image is imbibed into the pores of theanodized aluminum and sensitizer and carrier particles are removed withorganic solvent, the imaged anodized metal may be dipped into a suitabledye bath to form a complementary image, i.e. dye penetrates into thepores of the anodized aluminum containing no previous dye image and dyepenetrates into the pores of the anodized metal bearing the first dyeimage forming a complementary color. Typical of this would be theformation of a first cyan image, followed by dipping the anodized metalinto a yellow dye bath resulting in the formation of a green image on ayellow background. In this technique, the cyan portion of the imagewould be converted to green and the background area would be yellow.

The following examples are merely illustrative and should not beconstrued as limiting the scope of our invention:

EXAMPLE I A 15% by weight aqueous solution of polyvinyl alcohol (Elvanol71-30) was drawn down with a glass rod over the pores of an anodizedaluminum plate barely filling the pores of the anodized metal.Sixty-four one hundredths of a gram of Staybelite Ester #10 (partiallyhydrogenated rosin ester of glycerol), .19 gram benzil and .14 grame 4methyl 7 dimethylaminocoumarin dissolved in 100 mls. Chlorothene(1,1,1-trichloroethane) was applied to the polyvinyl alcohol filledanodized aluminum by flow coating the solution over the substratesupported at about a 60 angle with the horizonal. After air drying forone minute, the light-sensitive element was placed in contact with ayollow half-tone separation positive in a vacuum frame and exposed to acarbon are for about one minute. The light-sensitive element was removedfrom the vacuum frame and developed by rubbing a cotton pad containing atartrazine (yellow)-Pliolite VTL (vinyltoluene-butadiene copolymer) offrom about 1 to 15 microns diameter along the largest axis, across. theexposed element, thereby embedding the yellow developing powder into theunexposed areas of the light-sensitive layer. The excess powder wasremoved from the lightsensitive layer by impinging air at an angle ofabout 30 to the surface until the surface was substantially free ofpowder. The reproduction was then wiped with a fresh cotton padresulting in an excellent half-tone reproduction of the original yellowseparation transparency. The developed image was placed over a beaker ofboiling water for about 15 seconds during which time the yellow dyeimage was imbibed and molecularly dispersed in halftone, image-wiseconfiguration into the pores of the anodized aluminum. The molecularlydispersed image changed from a pale yellow to a more brilliant,saturated aesthetically pleasing yellow hue. The light-sensitive layerand Pliolite VTL developing powder on the surface of the anodizedaluminum plate were removed by flow coating Chlorothene clearingsolution over the layer leaving the yellow image in the pores of theanodized aluminum.

A second color was imbibed into the pores of the anodized aluminum byresensitizing the anodized aluminum with the same light-sensitivesolution used to develop the first yellow image, exposing thelight-sensitive element through the cyan separation positive, developedin the manner described above using a cyan developing powder composed of20% by weight Alphazurine 2G and by weight Pliolite VTL, the excessdeveloping powder was removed and the cyan image was molecularly imbibedinto the pores of the anodized aluminum by holding the element over abeaker of boiling water for about 15 seconds. The light-sensitive layerand Pliolite VTL developing powder were then removed by flowing Chloro-13 thene clearing agent over the surface of the developed image.

A magenta image was then deposited using the same light-sensitivesolution and the same technique except that a developing powder composedof 20% Carmoisine and 80% by weight Pliolite VTL was used. After themagenta dye was molecularly imbibed into the pores of the anodizedaluminum, the light-sensitive layer and Pliolite VTL developing powderwas removed by flowing Chlorothene over the anodized aluminum plate. Thepolyvinyl alcohol in the pores of the anodized aluminum was removed bywashing with cold tap water leaving the image in the pores of theanodized aluminum.

The developing powders employed in this example were prepared byball-milling for twenty-four hours 20 parts by weight of the appropriatedye and 80 parts by weight of Pliolite VTL.

EXAMPLE II This example illustrates the preparation of a decoratedanodized aluminum plate wherein no polyvinyl alcohol subbing layer wasemployed. One and ninety-two onehundredths of a gram Staybelite Ester#10, 0.77 gram benzil and 0.575 gram 4-methyl-7-dimethylaminocoumarindissolved in 100 mls. Chlorothene were flow coated over the bareanodized aluminum plate, exposed to actinic radiation through a cyanprinter for approximately one minute, developed with a 100% cyan dye inthe manner described in Example I, molecularly imbibed into the pores ofthe anodized aluminum in image-wise configuration by holding the elementover boiling water and the light-sensitive layer removed by flowingChlorothene over the anodized aluminum plate.

EXAMPLE III Example I was repeated except that the polyvinyl alcoholsubbing layer was applied by flow coating a .1% by weight polyvinylalcohol solution. The resultant images were somewhat splotchy indicatingthat either the thickness of the polyvinyl subbing layer had to beincreased in order to get a good image or the total solids in thelight-sensitive solution had to be increased in order for thelight-sensitive layer to protrude above the pores of the anodizedaluminum.

EXAMPLE IV Example II was repeated with essentially the same resultsexcept that the light-sensitive solution was composed of 2.88 gramsPiccolastic E-75 (modified polystyrene), 1.15 grams benzil and .432 gram4-methyl-7-dimethylaminocoumarin in 100 mls. Chlorothene and a 100%Carmoisine magenta dye was employed as the developing powder.

When this example was repeated using two-thirds the solids of thelight-sensitive solution described above, only an extremely weak imagewas formed indicating that it is necessary to employ a higher solid,light-sensitive solution or else partially fill the pores of theanodized aluminum in order to get a relatively strong saturated image inthe pores of the anodized aluminum.

Since many embodiments of this invention may be made and since manychanges may be made in the embodiments described, the foregoing isinterpreted as illustrative only and the invention is defined by theclaims appended hereafter.

What is claimed is:

1. The process of decorating anodized metals which comprises the stepsof exposing an anodized metal substrate bearing a light-sensitive layercapable of developing a R of 0.2 to 2.2 to actinic radiation inimage-wise configuration to establish a potential R of 0.2 to 2.2,applying a dry powder comprising a water-soluble dye to the exposedlight-sensitive layer, embedding the developing powder in image-wiseconfiguration into the light-sensitive layer, removing the developingpowder from the nonimage areas and molecularly imbibing and transportingsaid dye from the dry powder into the pores of the anodized metal inimage-wise configuration by contacting said light-sensitive element withwater vapor.

2. The process of claim 1, wherein the pores of the anodized metal areat least partially filled with a hydrophilic colloid.

3. The process of claim 1, wherein said light-sensitive layer is removedfrom the surface of the anodized metal with a solvent for thelight-sensitive layer after imbibing said dye into the pores of saidanodized metal.

4. The process of claim 1, wherein said light-sensitive layer is apositive-acting light-sensitive layer capable of developing a R of 0.4to 2.0.

5. The process of claim 4, wherein said dry powder comprises a carrierfor said water-soluble dye.

6. The process of decorating an anodized aluminum object which comprisesthe steps of exposing an anodized aluminum object bearing alight-sensitive layer, capable of developing an R of 0.2 to 2.2 toactinic radiation in image-wise configuration to establish a potential Rof 0.2 to 2.2, applying a dry powder comprising a watersoluble dye tothe exposed light-sensitive layer, embedding the developing powder inimage-wise configuration into the light-sensitive layer, removing thedeveloping powder from the non-image areas and molecularly imbibing andtransporting said dye from the dry powder into the pores of the anodizedmetal in image-wise configuration by contacting said light-sensitiveelement with water vapor and removing said light-sensitive layer with asolvent for said light-sensitive layer.

7. The process of claim 6, wherein after the light-sensitive element isremoved with a solvent for said light-sensitive layer, the anodizedmetal is sensitized with a second light-sensitive layer capable ofdeveloping a R of 0.2 to 2 .2, said second light-sensitive layer isexposed to actinic radiation in image-wise configuration to establish .apotential R of 0.2 to 2.2, developed with a second dry powder comprisinga second water soluble dye, said second powder is embedded into thesecond light-sensitive layer in image-wise configuration, developingpowder is removed from the non-image areas, and said second dye fromsaid second dry powder is molecularly imbibed and transported into thepores of the anodized metal in image-wise configuration by contactingsaid light-sensitive layer with water vapor.

8. The process of claim 7, wherein the pores of said anodized metal areat least partially filled with a hydrophilic colloid.

9. The process of claim '8, wherein said hydrophilic colloid is removedfrom the pores of said anodized aluminum after the last dye image isimbibed into the pores of said anodized metal.

10. The process of claim 7, wherein all of said lightsensitive layersare positive-acting, light-sensitive layers capable of developing a R of0.4 to 2.0.

11. The process of claim 10, wherein said powders comprise a carrier forsaid water-soluble dyes.

References Cited UNITED STATES PATENTS 2,384,857 9/1945 Terry 96-33NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant ExaminerU.S. Cl. X.R. 9617, 38.1, 35

